You can use the order() function directly without resorting to add-on tools -- see this simpler answer which uses a trick right from the top of the example(order) code:
R> dd[with(dd, order(-z, b)), ] b x y z 4 Low C 9 2 2 Med D 3 1 1 Hi A 8 1 3 Hi A 9 1 Edit some 2+ years later: It was just asked how to do this by column index. The answer is to simply pass the desired sorting column(s) to the order() function:
R> dd[ orderdd[order(-dd[,4], dd[,1]), ] b x y z 4 Low C 9 2 2 Med D 3 1 1 Hi A 8 1 3 Hi A 9 1 R> rather than using the name of the column (and with() for easier/more direct access).